The increasing need to integrate several contactless chips on a single substrate is making itself felt in particular because of growing demand for memory and security.
Integrating several chips on a single substrate does, however, pose the problem of overall dimensions which is linked to communication distances. In fact, contactless cards transmit their data with the aid of a magnetic field, the power of which depends on the size of their on-chip inductive antenna. Consequently, simply placing several contactless chips side-by-side on a single card means that each of them must have a bulky antenna in order to achieve an adequate communication range.
To overcome this problem, Document FR 2 812 482 proposes a contactless multi-chip card which comprises a collective antenna that forms a large surface-area inductive loop in order to obtain a significant communication range. Each of the contactless chips on the card then comprises an antenna which forms an inductive loop having a small surface area and located inside the collective antenna. The collective antenna thus acts as an intermediary for communicating with and powering the contactless chips.
Nevertheless, in this type of architecture, the collective antenna is used as an intermediary both for communication between the chips and the card's external environment (usually a contactless reader) and for inter-chip communication. It therefore follows that complex mechanisms must be provided in order to manage the stream of data that flows through the collective antenna.
In addition, in many applications, some chips are not designed to communicate with a reader located outside the card, only with other chips on the card. This includes arrangements of chips that form a memory assembly for data storage or chips tasked with communications security, such as cryptoprocessors for example.
Communication via just one collective antenna not only causes bandwidth and data collision problems when all communications have to transit via the collective antenna, communications between chips which are not designed to communicate with an external reader can be accessed by the reader and this can be harmful in terms of security in particular.